An RFID reader can read RFID tags that are within a particular range of the RFID reader. This range is generally a function of the RFID reader and more particularly a function of the capabilities of the reader's antenna. Further there may be occasions where the read range changes during operation of the reader for reasons that may include the provision of reduced power to the antenna due to the power remaining in the reader's battery. The read range of an RFID reader is also influenced by the “field of view” of the reader.
In current systems a user of an RFID reader must have historical knowledge of the reader's capability in order to guesstimate whether a particular tag, which may be present in a container, can be read. This process is inherently unpredictable as the user estimates the location of the tag and compares this to the knowledge of the reader's range. This unpredictability may lead to false negatives in the reading process where tags that are in fact present yet out of range of the reader are falsely determined as not being present. Further, any change in the range of the reader during operation will add to the unpredictability of the above process.
The operation of a typical RFID system is schematically illustrated in FIG. 1. An RFID reader 102 has an internal antenna (not shown) that allows the RFID reader 102 to provide an envelope 106 of RFID coverage associated with an antenna of the RFID reader 102. The envelope 106 represents the boundary of the RFID coverage. The shape of the envelope 106 is representational only and does not necessarily reflect the actual shape of the RFID coverage of the RFID reader 102. A first group of RFID tags 108 is present within the envelope 106, and will therefore be read by the RFID reader 102. Groups of tags 110 and 112 may possibly physically be located quite close to the group 108. However, if the groups 110 and 112 are located outside the envelope 106, they will not be read by the RFID reader 102. Thus without knowledge of the coverage of the RFID reader 102, the user may falsely determine that the tags 110 and 112 are not present.